In many general-purpose computer systems and in most commercial "word-processing" or document creation systems, the editing of textual data is performed by a human operator, using a typewriter-style keyboard to enter editing commands and data, and viewing the edited text on a CRT display. The computer maintains a "current position" in the text being edited, which most editing commands imply as an argument. For example, if the operator presses the "rubout" key, it is interpreted by the computer as a command to remove the character to the left of the current position from the text being edited and from the display of that text being viewed by the operator. The computer normally indicates the current editing position by displaying a distinctive marker, called the cursor, on the CRT along with the text being edited.
The operator controls the position of the cursor in a variety of ways. In the majority of such systems, a particular keystroke or combination of keystrokes is interpreted by the computer as a command to move the cursor to the right, left, up, or down in increments of a single character or, in some systems, an entire word, line or paragraph. In many systems, special keys are devoted to these functions and are usually located in a special keypad separate from and often adjacent to the typewriter keypad.
A smaller number of editing systems use a position-indicating device whose position is sensed by the computer and used to control the cursor position in the display and text being edited. Examples of such devices are: light pens, tablet pens, joysticks, thumb wheels, and "mice" (devices which sit on a table top and are moved about by hand). Devices of this type are disclosed in U.S. Pat. No. 3,541,521 to Koster, U.S. Pat. No. 3,541,541 to Engelbart and U.S. Pat. No. 3,835,464 to Rider.
All of the aforementioned prior art position-indicating devices enable an operator to "point" at a position on the display where the cursor is to be located. However, the typical editing sequence is; (1) manually adjust a control to position the cursor at the place to be edited; and (2) enter one or more keystrokes to modify the text. This sequence is then repeated for the next editing operation. If the operator needs to stop typing to pick up a light pen, or grasp a "mouse" or like device or to use a special keypad to adjust the cursor position, and then to return to the typewriter keyboard for the editing operation, he or she uses a lot of time getting his or her hands repositioned over the "home" typing keys. Often, one of the operator's hands is incorrectly positioned, upon return to the keyboard. For example, the operator's hand may have drifted one key to the right or left of the correct position, and many typing errors result. Touch typists especially find this type of interaction annoying, which is probably why such systems have found little acceptance outside of the computer research field.
Accordingly, it is an object of the present invention to provide a system for facilitating the generation of two-dimensional coordinate data for input to an electronic digital computer to control the position of a visible marker, or "cursor", displayed on the face of a cathode ray tube or other dynamic display device under control of the computer.
It is another object of the present invention to provide such a system which may be operated in conjunction with a typewriter-style keyboard in a manner which does not require the operator to remove a hand from the keyboard.
These and other objects and features of the present invention will be understood from the description to follow, taken in conjunction with the accompanying drawings.